1. Field of the Invention
The present invention relates to a display device, and more particularly, to a gray scale processing apparatus and method capable of enhancing a gray scale expression and minimizing an error diffusion noise.
2. Description of the Related Art
Recently, a plasma display panel (PDP), which facilitates fabrication of a large-sized panel, has come into notice as a flat panel display. The PDP reproduces pictures by adjusting the respective gas discharge periods of pixels depending on digital video data.
FIG. 1 is a perspective view illustrating a structure of a discharge cell in the related art PDP.
Referring to FIG. 1, the discharge cell of the PDP includes a sustain electrode pair 12A and 12B formed on an upper substrate 10 and a data electrode 20 formed on a lower substrate 18.
The sustain electrode pair 12A and 12B each have a double-layer structure of a transparent electrode and a metal electrode. The sustain electrode pair 12A and 12B are divided into a scan electrode 12A for supplying a scan signal for address discharge and a sustain signal for sustain discharge, and a sustain electrode 12B for supplying a sustain signal alternating with the scan electrode 12A. The data electrode 20 is formed to intersect with the sustain electrode pair 12A and 12B, and supplies a data signal for address discharge.
An upper dielectric layer 14 and a protective layer 16 are stacked on the upper substrate 10 on which the sustain electrode pair 12A and 12B are formed. The upper dielectric layer 14 and a lower dielectric layer 22 accumulate charges generated by discharge. The protective layer 16 prevents damage of the upper dielectric layer 14 by sputtering of plasma particles during the discharge and increases an emission efficiency of secondary electrons. Accordingly, a driving voltage applied from the outside can be lowered by the upper and lower dielectric layers 14 and 22 and the protective layer 16.
The lower dielectric layer 22 is formed on the lower substrate 18 where the data electrode 20 is formed. A barrier rib 24 is formed on the lower dielectric layer 22 with the data electrode 20 interposed therebetween. A phosphor layer 26 is formed on surfaces of the lower dielectric layer 22 and the barrier rib 24. The phosphor layer 26 includes a red (R) phosphor layer, a green (G) phosphor layer and a blue (B) phosphor layer. The phosphor layer 26 separates a discharge space to thereby prevent ultraviolet rays generated by gas discharge in the discharge space from leaking toward its neighboring discharge space. The phosphor layer 26 is radiated by ultraviolet rays generated by gas discharge to thereby emit R, G and B visible rays. The discharge space is charged with inert gases for gas discharge.
Although only one discharge cell is shown in FIG. 1, the PDP can also include a plurality of discharge cells arranged in matrix form.
A discharge cell is selected by address discharge of the data electrode 20 and the scan electrode 12A, and the selected discharge cell maintains discharge by sustain discharge by the sustain electrode pair 12A and 12B. During the sustain discharge, the phosphor 26 is radiated by ultraviolet rays generated in the selected discharge cell and thereby emits R, G and B visible rays. Accordingly, the discharge cell represents a gray scale by adjusting a sustain discharge period, namely the frequency of a sustain discharge according to video data. Combination of 3 discharge cells respectively coated with R, G and B phosphor layers 26 enables representation of a color of one pixel.
As an exemplary method of PDP driving method, there is an ADS (address and display separated) driving method that drives a PDP in such a way that an address period is separated from a display period, namely, a sustain period. The ADS driving method divides one frame 1F into a plurality of sub-fields SF1 through SF8 corresponding to respective bits of video data. Each of the sub-fields is then subdivided into a reset period RPD for initialization of a discharge cell, an address period APD for selection of a discharge cell, and a sustain period SPD for maintenance of the selected discharge cell's discharge. Different weights are given to sub-fields during the sustain period SPD, and the sustain periods are combined according to video data, whereby a gray scale is represented.
The PDP uses an error diffusing method so as to enhance an gray scale expression.
The error diffusing method calculates quantization error data of digital video data by using the Floyd-Steinberg error diffusing filter, applies different weights according to the calculated quantization error data and then diffuses the error to neighboring pixels.
For example, if an error diffusing operation about a current pixel P5 is performed as shown in FIG. 3, the error diffusing method gives a weight 1/16 to a pixel P1 neighboring the current pixel P5, a weight 5/16 to a pixel P2, a weight 3/16 to a pixel P3, and a weight 7/16 to a pixel P4, and thereby calculates error diffusion coefficients about the respective pixels P1 through P4. Thereafter, the error diffusing method generates a carry signal by adding the calculated error diffusion coefficients and then obtains a current pixel value by adding the carry signal to a current pixel value P5.
However, the error diffusing method has a problem in that error diffusion coefficients (that is, weights) about neighboring pixels are constantly set and repeated at every line and at every frame, whereby an error diffusing pattern is generated.
Further, the prior art error diffusing method has a limitation in a gray scale expression of video data.